Reconstituted asbestos matrix

ABSTRACT

An asbestos matrix suitable for use in a fuel cell or electrolysis cell is produced having a greater porosity and bubble pressure for a given thickness, improved homogeneity, and more uniform thickness than heretofore known. The matrix is produced by first shredding the asbestos; forming a slurry of the asbestos with water or a low boiling hydrocarbon, preferably an alcohol such as methanol; forming a mat by passing the slurry through a properly sized porous plaque having a piece of filter paper on top; drying the mat so produced; and rolling the mat so produced to yield desired thickness and surface finish.

United States Patent 1191 McBryar 1 Oct. 7, 1975 154] RECONSTITUTED ASBESTOS MATRIX 3,560,335 2/1971 Lueders 162/228 3,597,514 8/1971 .lager 4 t 162/153 [75] Inventor: McBrya" Dckmsoni 3,617,437 11/1971 Bagg et a1, l l 162/102 73, Assigns: The United states of America as 3,619,354 11/1971 Woolery 11 162/153 X rePfesenled by 9 United States FOREIGN PATENTS OR APPLlCATlONS /P l' 'f and Space 25,943 6/1914 United Kingdom 162/383 ,General 556,969 10/1943 United Kingdom 162/153 Counsel-Code GP, Washmgton, D.C. OTHER PUBLICATIONS 22 Ffl d; Jan 22 973 Casey, J. P., Pulp & Paper Making," lnterscience Publishers, Second Edition, Vol, 11, pp. 768, 813-815, 21 Appl, No.: 325,784

Primary ExaminerS. Leon Bashore [52] US. Cl. 162/102; 136/146; 136/148; Assistant Examiner-William F, Smith 162/153; 162/222; 162/228 Attorney, Agent, or Firm-Marvin J, Marnock; John [51 1 Int. Cl. D211] 5/18 R. Manning; Marvin F. Matthews [58] Field of Search 136/148, 146, 86 R;

[56] References Cited UNITED STATES PATENTS 1,979,864 11/1934 Carson 162/153 X 2,079,667 5/1937 Swift, Jrm. 162/228 2,802,405 8/1957 Krogel 4 A 162/102 2,963,397 12/1960 McLeod 1 162/228 X 2,971,878 2/1961 Heilman et a1... 162/181 C 3,028,911 4/1962 De Lear 162/383 3,185,906 5/1965 Hogue 162/153 X 3,297,516 1/1967 Naumann et a1. 163/3 3,325,349 6/1967 Reifers 162/383 X 3,342,642 9/1967 Barberm. 162/153 X 3,461,191 8/1969 Dale 162/153 X 3,549,488 12/1970 Phillips 162/228 FILTER BOX [57] ABSTRACT An asbestos matrix suitable for use in a fuel cell or electrolysis cell is produced having a greater porosity and bubble pressure for a given thickness, improved homogeneity, and more uniform thickness than heretofore known. The matrix is produced by first shredding the asbestos; forming a slurry of the asbestos with water or a low boiling hydrocarbon, preferably an alcohol such as methanol; forming a mat by passing the slurry through a properly sized porous plaque having a piece of filter paper on top; drying the mat so produced; and rolling the mat so produced to yield desired thickness and surface finish.

9 Claims, 1 Drawing Figure 6 WATER MANOMETER U.S. Patent Oct. 7,1975

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kmt MEOZQE Qmk QR m XOQ Qmk it RECONSTITUTED ASBESTOS MATRIX ORIGIN OF THE INVENTION The invention described herein was made by an employee of the United States Government and may be manufactured and used by and for the Government of the United States of America for governmental purposes without the payment of any royalites thereon or therefor.

BACKGROUND OF THE INVENTION I. Field of the Invention The present invention is directed to a reconstituted asbestos matrix for use in a fuel cell or an electrolysis cell. In principle, any reduction/oxidation chemical reaction can be used as the basis of fuel cell design. The best known, and those which have received the most developmental attention, are based on chemicals that offer ready sources of hydrogen and oxygen. The simplest, most highly developed, and most efficient of these is the gaseous hydrogen/oxygen fuel cell.

In such a fuel cell, hydrogen is fed to the fuel electrode (anode), where it is adsorbed and dissociated forming hydrogen ions and releasing electrons to the load circuit. Thus the anode reaction is an oxidation reaction. At the cathode, oxygen is adsorbed and dissociated, then combines with water (which is also dissociated in the process) and electrons from the load circuit. Thus the cathode reaction is a reduction reaction. In an acidic cell, the cathode reaction produces peroxide ions; in an alkaline cell, hydroxyl ions. In an acidic cell, the hydrogen ions formed at the anode migrate through the electrolyte to the cathode where they combine with the peroxide ions to form product water, thus completing the circuit. In an alkaline cell, hydroxyl ions migrate from the cathode through the electrolyte to the anode where they combine with the hydrogen ions to form product water, thus completing the circuit. Chemical reactions which occur in the alkaline cell during this process are:

At the anode:

H- 2 OH At the cathode:

The electrolyte ofa fuel cell must be immobilized in some manner so that it is not washed out of the cell with the product water (or other reaction product, depending upon the fuel and oxidant used). Methods utilized for this function are varied, such as the use of solid membranes possessing ionic properties, and the use of small pore electrodes in conjunction with opposing gas pressures which balance the capillary forces of the small pores, thus creating a static condition for the electrolyte.

The present invention relates to the asbestos capillary matrix as a medium for alkaline electrolyte immobilization. Asbestos has been used for years as a matrix material due to its compatibility with caustic media, and due to its fibrous nature which permits formation into thin mats while exhibiting a great affinity (capillarity) for liquid (alkaline electrolyte) media. The matrix material must possess a high degree of physical integrity in very thin sheets since it is desirable to position the electrodes as close together as possible in order to keep the internal resistance small (or to maximize ionic conductivity). The matrix must also have a high porosity (high void volume with respect to total volume), in conjunction with small pore size in order to produce the high capillarity required to retain the electrolyte. The only material available to the developers of the capillary matrix fuel cells has been commercially available, asbestos sheets which are manufactured on papermaking machinery. It was determined in attempting to extend operating life and improve electrical performance to meet the long duration, high power applications of the space program, that these commercially available asbestos sheets were a serious limiting factor. By reconstituting the commercially available material according to the present invention as described hereinafter, several advantages were realized:

a. Bubble pressure was essentially doubled or tripled for a given thickness;

b. Porosity was increased (less dense material while increasing bubble pressure);

c. Homogeneity was improved;

d. Thickness was more unifomi.

2. Prior Art The following patents were located in a novelty search for the present invention:

US. Pat. No. 3,l85,906

US. Pat. No. 3,342,642.

SUMMARY OF THE INVENTION The present invention is directed to a process for the production of an asbestos matrix suitable for use in a fuel cell. More specifically, the process comprises shredding of commercial asbestos material, forming a slurry of dispersed asbestos fibers in a low boiling liquid, passing the slurry through a porous plaque, filtering out the asbestos fibers to form a matrix having any desired thickness from about 0.010 inches to 0.050 inches, vacuum drying the matrix so produced, and rolling the mat for final thickness and surface smoothing. It is preferred to utilize commercially available asbestos material from .lohns-Manville Products Corporation which has been purified and treated for this particular end use. By reconstituting the asbestos matrix according to the present invention, a product having greater porosity, higher bubble pressure, and more uniform thickness is produced.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic drawing of the apparatus which may be used in the process for the production of the asbestos matrices according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The fundamental components of a fuel cell are two electrodes (an anode and a cathode) and an electrolyte. The electrolyte is conventionally confined in a compartment defined by the two electrodes which are held separated by insulation gaskets. The electrolyte serves as an electrical insulator for the electrodes and as an ionic conductor which transports ionized species between the two electrodes, an essential reaction mechanism of the operating fuel cell. In other words, the electrolyte is electrcally insulative and ionically conductive. The electrolyte used in the capillary matrix fuel cell is characteristically a solution of about 30 to 45 percent potassium hydroxide (KOH) which is in the liquid phase from about 40C. throughout the operating temperature range of the fuel cellv This liquid is held in place between the electrodes by the capillary action of an asbestos matrix which is in the form of a fibrous mat chemically composed principally of magnesium silicate (MgSiO This material is chemically stable under the conditions imposed. The asbestos matrix must be uniform in thickness and sectional density, must possess sufficiently high strength to withstand the compressive forces of a stacked and packaged group of cells, and must possess sufficiently high capillarity to efficiently contain the electrolyte against differential reactant gas pressures which can inadvertently occur during normal fuel cell handling and operation. If the matrix does not retain the electrolyte during a gas pressure excursion. electrolyte can be displaced from the matrix, gas cross-over can occur and mix with the other reactant gas, and the two gases will react directly on the catalytic surface of the electrode in a manner which results in liberation of theoretical quantities of energy (68 kilocalories/mole of H which is manifested in the form of a fire. This is destructive to the fuel cell materials of construction and the result is the end-of-life of the fuel cell.

It is the object of the present invention therefore to increase the performance and to extend the useful operating life of alkaline capillary matrix fuel cells and electrolysis cells by improving the structural integrity and reliability by a process for the production of an improved asbestos matrix in a new and unique manner. Johns-Manville Products Corporation has been the only supplier of asbestos matrix material that is suitable for use in fuel cells. The material is manufactured on paper-making machinery to specified thicknesses normally used in fuel cells (e.g.. 0.010 inches to 0.050 inches in 0.010 inch increments). The uniformity of matrix material produced by this method has been determined to be inadequate for use in fuel cells for long life (over approximately 2,000 hours), high power (over approximately 800 Watts per square foot), and tolerance to inadvertent overpressure conditions. The ability of the matrix to contain electrolyte is limited by the largest pore (lowest capillary force) and the thinnest portion of the matrix. Simply increasing the thickness of the matrix to improve these parameters is unac ceptable because ionic resistance increases proportion ately with the thickness of the matrix which reduces power output.

According to the present invention, the process provides a method for forming fuel cell electrolyte matrices using asbestos. Preferably, the asbestos used in fuel cell grade asbestos from .lohns-Manvillc, I945 Chrysotile asbestos. mined in Arizona. The basic procedure involves shredding the asbestos, forming an asbestos slurry. forming an asbestos matrix, drying the matrix. and rolling the matrix so produced. The shredding is accomplished by tearing the asbestos into approximately l inch squares and placing it in a blender wherein the dry asbestos is shredded. In the preferred procedure the dry asbestos is weighed so that the desired amount will be present in the resulting reconstituted asbestos matrix (or mat), herein referred to as a RAM. The weighed quantity of asbestos is then mixed with a low boiling hydrocarbon preferably an alcohol such as methanol. However, water or other low boiling materials such as ketones or the like may be used.

To form the asbestos matrix of the present invention, a slurry is formed with the shredded asbestos and water. or a low boiling hydrocarbon, preferably methanol, and passed through a porous plaque which can be sintered nickel plaque or a borosilicate glass frit plaque having a pore size of 25 to microns. The porous nickel plaque is formed from metal such as nickel by taking the powdered metal of the appropriate size and sintering under an inert gas atmosphere to form the porous filtering plaque. The final pore size is produced by rolling the plaque which squeezes the particles, thus reducing pore size. The range of particle size of the metal, preferably powdered nickel, or example, is between l0 and lOO microns and is sintered and pressed into a size and shape appropriate for the particular filter box used in making the asbestos matrices. The asbestos matrix is formed by drawing the liquids from the asbestos slurry in the filter box through the porous plaque.

To illustrate more specifically the process of the present invention and all of its details, the following specific procedure for forming RAMs is set forth as follows with references made to the drawing. As shown in the drawing, a filter box 1 has an outlet connected to an aspirator bottle 2 which is connected by a glass rod 3 and drain hose 4. The aspirator bottle 2 is set on a lower surface than the filter box 1. Line 5 is a vacuum line which draws the liquid in the slurry placed in the filter box I through the porous plaque positioned in the filter box 1 and through the drain line 4 into the aspirator bottle 2. in vacuum line 5 is a water manometer 6 for measuring the vacuum connected by tee 7. By means of tee 8, line 5 is connected to vacuum pump 9 and a relief valve, V ID. The dimensions and quantities are given only as they applied to the particular application under which the process was developed and represent a specific example and are not intended to be limiting. l.0 Fabrication Procedure l.l Shredding the Asbestos l .l l Place up to 7 gm of asbestos torn into approximately 1 inch squares into a blender.

.l.2 Set the speed selector of the blender corresponding to a no-load speed of approximately 18500 RPM.

.13 Turn on the blender for ID to l2 seconds and shred the asbestos. Turn off the blender.

.l.4 Store shredded asbestos in a clean, covered container.

.l.5 Repeat steps l through 4 until a desired quantity of asbestos is accumulated.

Forming the Slurry .2.1 Weight out the desired quantity of asbestos. The desired quantity of asbestos is the desired grams of asbestos/in to be contained in the finished RAM plus the grams of asbestos/in lost in the fabrication process (determined by experimentation). EXAMPLE: If the finished RAM is to contain 0.25 gms asbestos/i11 and the filter box area equals 53.8 in, the quantity of asbestos for the mat 0.25 gm/in X 53.8 in l3.45 grns The quantity of asbestos lost in the process:

0.006 gms/n X 53.8 in 0.323 grams Thus, the desired quantity of asbestos to be weighed out is:

13.45 gms +0323 grns l3.773 gms.

or 13.77 grams (rounded off). The tolerance on the desired quantity of asbestos to be weighed out is i 0.05 grams.

2.2 Place the desired quantity of asbestos in the blender.

2.3 Pour into the blender 80 :5 ml of methanol per gram of asbestos added in 1.2.2. Close the blender.

2.4 Set the speed selector for the lowest blender speed.

2.5 Turn on the blender.

2.6 Move the speed selector to the setting corresponding to a no-load speed of approximately 18500 RPM.

.2.7 Blend the asbestos/alcohol slurry for 30 to 35 seconds (at the high setting).

2.8 Move the speed selector to the lowest speed setting. .29 Turn off the blender.

.2. l0 Pour the contents from the blender into a 4L evacuation flask.

.2.] l Deaerate the asbestos/alcohol slurry for 1 minute at 22 to 23 inches of water vacuum. Agitate the evacuation flask during deaeration to help remove gas bubbles trapped in the slurry. 1.3 Forming the Matrix .3.] Perform this operation at least 1 hour before forming the first matrix:

Place a sufficient quantity of properly sized No. 4 Whatman filter papers in a covered tray. Pour methanol in the tray, covering the papers. The filter paper must be soaked in methanol at least 1 hour prior to using to prevent wrinkling of the paper during the forming of the asbestos matrix.

.32 Open the filter box 1.

.33 Fill the lower half of the filter box I with methanol by pouring same through the filter support screen, stopping when the screen is just covered with methanol. Make sure the drain hose 4 is held above the top of the filter box 1.

.3.4 Lay a properly sized porous nickel plaque on top of the support screen in the filter box.

3.5 Take one of the filter papers from the glass tray (See Step 1.3.1) and lay it on the porous nickel plaque.

3.6 Pour the asbestos/alcohol slurry from Step 1.2. 1 1 into the filter box on top of the filter paper.

.3.7 With a inch (or any convenient size) diame ter glass stirring rod. stir the slurry lengthwise and then cross-wise to remove air bubbles. Shake the filter box 1 in a cross-wise motion to reduce the traces of stirring. The surface of the slurry should have a smooth, uniform appearance.

3.8 Close the filter box 1.

.3.9 Connect the filter box drain hose 4 to a 4L aspirator bottle 2 and apply a vacuum. Adjust the bleed valve (V,) such that the maximum vacuum is inches to 25 inches of water. Once this valve has been adjusted, additional adjustments are generally not required during subsequent matrix formings. 3.11) Allow the alcohol to drain for 10 to 12 min- LIKES.

.3. l 1 Open the filter box I and remove the asbestos matrix and filter paper.

1.4 Drying the Asbestos Matrix (Unleached Asbestos) .4.1 Lay a plastic board on the wet asbestos matrix (Step 1.3.1 1 J and invert the assembly.

.4.2 Carefully remove the filter paper.

' commercially available matrices from 5 1.5 Drying the Asbestos Matrix (Leached Asbestos) 1.5.1 Lay a plastic board on the wet asbestos matrix (Step 1.3.1 1) and invert the assembly.

1.5.2 Carefully remove the filter paper.

1.5.3 Dry the asbestos on the plastic board at room temperature. (Approximately 4 hours) 1.5.4 Place each dry asbestos matrix in a clean plastic bag which has been properly identified.

To illustrate the advantages of the RAMs made according to the present invention as compared with the John- Manville Products Corporation and which are made by conventional paper-making machinery, data is presented in Table I.

TABLE 1 Bubble Material Thickness Porosity Pressure Unit Weight (.UUl") 1) (t g) (ti/in 95 J.M. 1U 5U 15 .13 2e 50 .27 3U 5U 55 .40

RAM 1t) 70 35 .15

Values are incraged. lndi\idu.'|l \alues are quite variable between samples as recched from 1M. IndMdual \alues on \arious samples are quite consistent for RAM.

The nature and objects of the present invention having been completely described and illustrated and a viable manufacturing mode thereof contemplated set shredding a given quantity of asbestos material to form a non-matted bulk material of separated asbestos fibers;

forming a homogeneous randomly oriented slurry of said asbestos fibers in water or a low boiling liquid hydrocarbon to provide a uniform dispersion of the fibers in the water or liquid hydrocarbon;

deaerating said slurry by stirring and agitating the slurry to remove air bubbles and subjecting the slurry to a vacuum environment while stirring;

filtering out the asbestos fibers through a filter paper and porous plaque by drawing off the deaerated liquid of the slurry through the filter paper and plaque by applying a vacuum and leaving randomly oriented uniformly distributed asbestos fibers on the paper to form a homogeneous matrix of a thick ness within a predetermined range of thickness and a uniformly constant porosity wherein the volume of interstices in the material exceeds the volume of its mass to provide a porosity ratio of substantially stripping the asbestos matrix from the filter paper and plaque; and

vacuum drying the matrix so produced.

2. The process for production of an asbestos matrix s defined in claim 1, including the further step of rolling the matrix so produced to smooth out the rippled surface thereof and to obtain the desired final thickness of the matrix.

3. A process according to claim 2 wherein said hy- 7. A process according to claim 2 wherein the pores drocarho" is illcnhQL I range from 25 to 75 microns.

4. A process according to claim 2 wherein said hy- 8. A pmcess according to claim 2 wherein Said drocarbon is methanol.

. rous plaque Is a frittered glass plaque. 5. A process according to claim 2 wherein bklld po- 5 9 mus plaque is a simered metal plaque. A process according to clalm 2 whereln said po- 6. A process according to claim 2 wherein said pop q is 11 Sodium borosilicati: glass P q rous plaque is a sintercd nickel plaque. 

1. A PROCESS FOR THE PRODUCTION OF AN ASBESTOS MATRIX SUITABLE FOR USE IN A FUEL CELL WHICH COMPRISES: SHREDDING A GIVEN QUANTITY OF ASBESTOS MATERIAL TO FORM A NON-MATTED BULK MATERIAL ASBESTOS FIBERS, FORMING A HOMOGENEOUS RANDOMLY ORIENTED SLURRY OF SAID ASBESTOS FIBERS IN WATER OR A LOW BOILING LIQUID HYDROCARBON TO PROVIDE A UNIFORM DISPERSION OF THE FIBERS IN THE WATER OR LIQUID HYDROCARBON, DEAERATING SAID SLURRY BY STTIRRING AND AGITATING THE SLURRY TO REMOVE AIR BUBBLES AND SUBJECTING THE SLURRY TO A VACUUM ENVIRONMENT WHILE STIRRING: FILTERING OUT THE ASBESTOS FIBERS THROUGH A FILTER PAPER AND POROUS PLAQUE BY DRAWING OFF THE DEARATED LIQUID OF THE SLURRY THROUGH THE FILTER PAPER AND PLAQUE NBY APPLYING A VACUUM AND LEAVING RANDOMLY ORIENTED UNIFORMLY DISTURBUTED ASBESTOS FIBERS ON THE PAPER TO FORM A HOMOGENEOUS MATRIX OF A THICKNESS WITHIN A PREDETERMINED RANGE OF
 2. The process for production of an asbestos matrix as defined in claim 1, including the further step of rolling the matrix so produced to smooth out the rippled surface thereof and to obtain the desired final thickness of the matrix.
 3. A process according to claim 2 wherein said hydrocarbon is an alcohol.
 4. A process according to claim 2 wherein said hydrocarbon is methanol.
 5. A process according to claim 2 wherein said porous plaque is a sintered metal plaque.
 6. A process according to claim 2 wherein said porous plaque is a sintered nickel plaque.
 7. A process according to claim 2 wherein the pores range from 25 to 75 microns.
 8. A process according to claim 2 wherein said porous plaque is a frittered glass plaque.
 9. A process according to claim 2 wherein said porous plaque is a sodium borosilicate glass frit plaque. 